Poly(4-hydroxystyrene-co-4-methoxystyrene) (MEOST) was synthesized and MEOST-13 with the methoxystyrene content of 12.5 mol % was used as a binder polymer for a three-component photopolymer system. The MEOST-13 films containing a vinyl ether monomer and a photoacid generator are insolubilized in an aqueous base in a prebake step owing to the thermal crosslinking reaction between hydroxyl groups of MEOST-13 and vinyl ether groups. Upon exposure to light and subsequent postexposure bake, the crosslinks are decomposed by photogenerated acids, leading to effective solubilization of the exposed areas. The MEOST-13 films showed sufficient insolubilization at baking temperatures of 140 degreesC or above. The conversion of vinyl ether groups increased rapidly with increasing baking temperature. The sensitivity of the MEOST-13 films increased abruptly with an increase in postexposure bake temperature because of the nature of chemical amplification. The MEOST-13 films showed a sensitivity of 33 mJ/cm(2) and afforded positive-tone images with the improved resolution of 0.30-mum line and space at 248-nm light.